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.Dd August 23, 2020
.Dt MINCORE 2
.Os
.Sh NAME
.Nm mincore
.Nd determine residency of memory pages
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mincore "const void *addr" "size_t len" "char *vec"
.Sh DESCRIPTION
The
.Fn mincore
system call determines whether each of the pages in the region beginning at
.Fa addr
and continuing for
.Fa len
bytes is resident or mapped, depending on the value of sysctl
.Va vm.mincore_mapped .
.\"The beginning address,
.\".Fa addr ,
.\"is first rounded down to a multiple of the page size (see
.\".Xr getpagesize 3 ) .
.\"The end address,
.\".Fa addr No + Fa len ,
.\"is rounded up to a multiple of the page size.
The status is returned in the
.Fa vec
array, one character per page.
Each character is either 0 if the page is not resident, or a combination of
the following flags (defined in
.In sys/mman.h ) :
.Bl -tag -width ".Dv MINCORE_REFERENCED_OTHER"
.It Dv MINCORE_INCORE
Page is in core (resident).
.It Dv MINCORE_REFERENCED
Page has been referenced by us.
.It Dv MINCORE_MODIFIED
Page has been modified by us.
.It Dv MINCORE_REFERENCED_OTHER
Page has been referenced.
.It Dv MINCORE_MODIFIED_OTHER
Page has been modified.
.It Dv MINCORE_PSIND(i)
Page is part of a large
.Pq Dq super
page with size given by index
.Dv i
in the array returned by
.Xr getpagesizes 3 .
.It Dv MINCORE_SUPER
A mask of the valid
.Dv MINCORE_PSIND()
values.
If any bits in this mask are set, the page is part of a large
.Pq Dq super
page.
.El
.Pp
The information returned by
.Fn mincore
may be out of date by the time the system call returns.
The only way to ensure that a page is resident is to lock it into memory
with the
.Xr mlock 2
system call.
.Pp
If the
.Va vm.mincore_mapped
sysctl is set to a non-zero value (default), only the current process'
mappings of the pages in the specified virtual address range are examined.
This does not preclude the system from returning
.Dv MINCORE_REFERENCED_OTHER
and
.Dv MINCORE_MODIFIED_OTHER
statuses.
Otherwise, if the sysctl value is zero, all resident pages backing the
specified address range are examined, regardless of the mapping state.
.Sh IMPLEMENTATION NOTES
Prior to the introduction of
.Dv MINCORE_PSIND()
in
.Fx 13.0 ,
.Dv MINCORE_SUPER
consisted of a single bit equal to
.Dv MINCORE_PSIND(1) .
In particular, applications compiled using the old value of
.Dv MINCORE_SUPER
will not identify large pages with size index 2 as being large pages.
.Sh RETURN VALUES
.Rv -std mincore
.Sh ERRORS
The
.Fn mincore
system call will fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
The virtual address range specified by the
.Fa addr
and
.Fa len
arguments is not fully mapped.
.It Bq Er EFAULT
The
.Fa vec
argument points to an illegal address.
.El
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr mlock 2 ,
.Xr mprotect 2 ,
.Xr msync 2 ,
.Xr munmap 2 ,
.Xr getpagesize 3 ,
.Xr getpagesizes 3
.Sh HISTORY
The
.Fn mincore
system call first appeared in
.Bx 4.4 .
